Airfoil with variable profile responsive to thermal conditions

ABSTRACT

An airfoil includes an airfoil body having a first section and a second section that differ in coefficient of thermal expansion by at least 10% and that each have a through-thickness that is 20% or greater than a through-thickness of the airfoil body. The second section is arranged in thermomechanical juxtaposition with the first section such that the first section and the second section cooperatively thermomechanically control a profile of the airfoil body responsive to varying thermal conditions.

CROSS-REFERENCE TO RELATED APPLICATION

The present disclosure is continuation of U.S. patent application Ser.No. 13/728,075, filed Dec. 27, 2012.

BACKGROUND

This disclosure relates to airfoils. Gas turbine engines and otherturbomachines include airfoils in the form of static vanes and rotatableblades. The shape of the airfoils can change based on the operationalconditions with respect to stress loads, thermal expansion/contractionand other factors. Typically, the airfoils are designed to particularoperational conditions for optimum performance at those conditions.

SUMMARY

An airfoil according to an exemplary aspect of the present disclosureincludes an airfoil body having a first section and a second sectionthat differ by coefficient of thermal expansion. The second section isarranged in thermomechanical juxtaposition with the first section suchthat the first section and the second section cooperativelythermomechanically control a profile of the airfoil body responsive tovarying thermal conditions.

In a further non-limiting embodiment of any of the foregoing examples,the first section and the second section differ by composition.

In a further non-limiting embodiment of any of the foregoing examples,the first section and the second section are different compositionmetallic materials.

In a further non-limiting embodiment of any of the foregoing examples,the first section and the second section are different compositionsselected from aluminum, aluminum alloys, titanium, titanium alloys,iron, iron alloys, nickel, nickel alloys, cobalt, cobalt alloys andcombinations thereof.

In a further non-limiting embodiment of any of the foregoing examples,the first section and the second section each have a through-thicknessthat is 20% or greater than a through-thickness of the airfoil body.

A further non-limiting embodiment of any of the foregoing examplesincludes a distinct boundary between the first section and the secondsection.

A further non-limiting embodiment of any of the foregoing examplesincludes a compositional gradient boundary between the first section andthe second section.

In a further non-limiting embodiment of any of the foregoing examples,the first section is a core and the second section is a shellcircumscribing the core.

In a further non-limiting embodiment of any of the foregoing examples,the core terminates at an intermediate span between ends of the airfoilbody.

In a further non-limiting embodiment of any of the foregoing examples,the core tapers along a span-wise direction of the airfoil body.

In a further non-limiting embodiment of any of the foregoing examples,one of the first section and the second section has a suction sidesurface of the airfoil body and the other of the first section and thesecond section has a pressure side surface of the airfoil body.

In a further non-limiting embodiment of any of the foregoing examples,at least one of the first section and the second section includes across-pattern.

In a further non-limiting embodiment of any of the foregoing examples,one of the first section and the second section has a pressure sidesurface and an opposed suction side surface, and the other of the firstsection and the second section partially covers at least one of thepressure side surface and the suction side surface.

A turbomachine according to an exemplary aspect of the presentdisclosure includes an airfoil that has an airfoil body having a firstsection and a second section that differ by coefficient of thermalexpansion. The second section is arranged in thermomechanicaljuxtaposition with the first section such that the first section and thesecond section cooperatively thermomechanically control a profile of theairfoil body responsive to varying thermal conditions.

A further non-limiting embodiment of any of the foregoing examplesincludes a turbine section that has the airfoil.

A further non-limiting embodiment of any of the foregoing examplesincludes a compressor section and a combustor in fluid communicationwith the compressor section, the turbine section in fluid communicationwith the combustor.

A method of controlling an airfoil profile according to an exemplaryaspect of the present disclosure includes controlling a profile of anairfoil body in response to varying thermal conditions bythermomechanically juxtaposing a first section and a second section ofthe airfoil body that differ by coefficient of thermal expansion.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the present disclosure willbecome apparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

FIG. 1 illustrates an example turbomachine.

FIG. 2 illustrates an example airfoil of a turbomachine.

FIG. 3 illustrates a sectional view of the airfoil of FIG. 2.

FIG. 4 illustrates a plan view of a portion of the airfoil of FIG. 2.

FIG. 5 illustrates another example airfoil.

FIG. 6 illustrates another example airfoil.

FIG. 7 illustrates another example airfoil.

FIGS. 8-10 illustrate further example airfoils.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a turbomachine 20. In this example, theturbomachine 20 is a gas turbine engine, which is disclosed herein as atwo-spool turbofan that generally incorporates a fan section 22, acompressor section 24, a combustor section 26 and a turbine section 28.Alternative engines might include an augmentor section (not shown) amongother systems or features. The fan section 22 drives air along a bypassflowpath while the compressor section 24 drives air along a coreflowpath for compression and communication into the combustor section 26then expansion through the turbine section 28. Although depicted as aturbofan gas turbine engine in the disclosed non-limiting embodiment, itshould be understood that the concepts described herein are not limitedto use with turbofans and the teachings may be applied to other types ofturbomachines, including three-spool engine architectures, ground-basedengines, air cycle machines, vacuum pumps and the like.

The turbomachine 20 generally includes a first spool 30 and a secondspool 32 mounted for rotation about an engine central axis A relative toan engine static structure 36 via several bearing systems 38. It shouldbe understood that various bearing systems 38 at various locations mayalternatively or additionally be provided.

The first spool 30 generally includes a first shaft 40 thatinterconnects a fan 42, a first compressor 44 and a first turbine 46.The first shaft 40 is connected to the fan 42 through a gear assembly ofa fan drive gear system 48 to drive the fan 42 at a lower speed than thefirst spool 30. The second spool 32 includes a second shaft 50 thatinterconnects a second compressor 52 and second turbine 54. The firstspool 30 runs at a relatively lower pressure than the second spool 32.It is to be understood that “low pressure” and “high pressure” orvariations thereof as used herein are relative terms indicating that thehigh pressure is greater than the low pressure. An annular combustor 56is arranged between the second compressor 52 and the second turbine 54.The first shaft 40 and the second shaft 50 are concentric and rotate viabearing systems 38 about the engine central axis A which is collinearwith their longitudinal axes.

The core airflow is compressed by the first compressor 44 then thesecond compressor 52, mixed and burned with fuel in the annularcombustor 56, then expanded over the second turbine 54 and first turbine46. The first turbine 46 and the second turbine 54 rotationally drive,respectively, the first spool 30 and the second spool 32 in response tothe expansion.

The turbomachine 20 is a high-bypass geared aircraft engine that has abypass ratio that is greater than about six (6), with an exampleembodiment being greater than ten (10), the gear assembly of the fandrive gear system 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3:1 and the first turbine 46 has a pressure ratio that isgreater than about five (5). The first turbine 46 pressure ratio ispressure measured prior to inlet of first turbine 46 as related to thepressure at the outlet of the first turbine 46 prior to an exhaustnozzle. The first turbine 46 has a maximum rotor diameter and the fan 42has a fan diameter such that a ratio of the maximum rotor diameterdivided by the fan diameter is less than 0.6. It should be understood,however, that the above parameters are only exemplary.

A significant amount of thrust is provided by the bypass flow due to thehigh bypass ratio. The fan section 22 of the turbomachine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet, with the engine at its best fuel consumption. To makean accurate comparison of fuel consumption between engines, fuelconsumption is reduced to a common denominator, which is applicable toall types and sizes of turbojets and turbofans. The term is thrustspecific fuel consumption, or TSFC. This is an engine's fuel consumptionin pounds per hour divided by the net thrust. The result is the amountof fuel required to produce one pound of thrust. The TSFC unit is poundsper hour per pounds of thrust (lb/hr/lb Fn). When it is obvious that thereference is to a turbojet or turbofan engine, TSFC is often simplycalled specific fuel consumption, or SFC. “Low fan pressure ratio” isthe pressure ratio across the fan blade alone, without a Fan Exit GuideVane system. The low fan pressure ratio as disclosed herein according toone non-limiting embodiment is less than about 1.45. “Low corrected fantip speed” is the actual fan tip speed in feet per second divided by anindustry standard temperature correction of [(Tram ° R)/(518.7 °R)]^(0.5). The “Low corrected fan tip speed” as disclosed hereinaccording to one non-limiting embodiment is less than about 1150 feetper second.

The turbine section 28 of the turbomachine 20 includes an airfoil 60.The airfoil 60 is a rotatable blade in this example, although it is tobe understood that the airfoil 60 can alternatively be a static vane orcan be a blade or vane in another section of the turbomachine 20.

Airfoils can experience varying thermal and pressure conditions inoperation, such as temperature/pressure variations at different flightstages or temperature/pressure variations radially across the surfacesof the airfoil. Airfoils can be designed to have a particular geometryprofile at given design point conditions to achieve a desiredaerodynamic performance. However, the profile of the airfoil changeswith changing thermal conditions due to thermal expansion/contraction,rotational speed, pressure loading, etc. Thus, the profile varies fromthe design point to a profile that may not provide as good aerodynamicperformance. In this regard, as will be described in further detailbelow, the airfoil 60 provides for passive profile control in order toachieve more desirable profiles at varied thermal conditions.

FIG. 2 shows an isolated view of one of the airfoils 60. Again, althoughthe airfoil 60 is shown herein as a blade, the examples are alsoapplicable to vanes and other components of a gas turbine engine. Theairfoil 60 includes an airfoil body 62 that generally extends between aleading edge LE and a trailing edge TE, a first end 64 (i.e., tip) and asecond end 66 (i.e., root), and a first side surface 68 and a secondside surface 70. In this example, the first side surface 68 is apressure side surface and the second side surface 70 is a suction sidesurface. In this example, the airfoil body 62 is connected to a rootportion 72, for mounting the airfoil 60 in a known manner.

FIG. 3 shows a sectioned view of the airfoil 60 according to FIG. 2 andFIG. 4 shows a side view of a portion of the airfoil body 62. Theairfoil body 62 includes a first section 74 and a second section 76 thatdiffer by coefficient of thermal expansion. The sections 74/76 arearranged in thermomechanical juxtaposition to cooperativelythermomechanically control a profile P (FIG. 2) of the airfoil body 62responsive to varying thermal conditions. One or more additionalsections that differ from sections 74/76 by coefficient of thermalexpansion can also be used in thermomechanical juxtaposition to one orboth of sections 74/76 to further cooperatively thermomechanicallycontrol a profile P of the airfoil body 62. In this example, the secondsection 76 is a core and the first section 74 is a shell thatcircumscribes the core 76. For example, the second section 76 can extendentirely from the first end 64 to the second end 66.

The sections 74/76 differ by composition to achieve the difference incoefficient of thermal expansion. In one example, the compositions ofthe sections 74/76 are different metallic materials. For example, themetallic materials are different materials selected from aluminum,aluminum alloys, titanium, titanium alloys, iron, iron alloys, nickel,nickel alloys, cobalt, cobalt alloys or combinations thereof.

Upon heating or cooling from a given temperature, the sections 74/76thus differentially expand or contract. The difference in thermalcontraction or expansion between the sections 74/76 has the tendency todistort the profile P of the airfoil body 62. By selecting thecompositions, and therefore the coefficients of thermal expansion, thedistortion, or lack thereof, can be controlled responsive to the varyingthermal conditions. In one example, the coefficients of thermalexpansion differ by at least 10%.

For instance, in the given example with the core/shell geometry, if thesecond section 76 were to have a higher coefficient of thermal expansionthan the first section 74, the profile P of the airfoil body 62 wouldhave a tendency to change from the illustrated contour upon an increasein temperature. Thus, the sections 74/76 cooperativelythermomechanically control the profile P responsive to the varyingthermal conditions. As can be appreciated, the geometries andcompositions of the sections 74/76 can be designed to achieve a desireddegree of distortion, distortion to a desired profile, or used tocompensate for other loads to minimize or even eliminate distortion overa temperature range.

The thermomechanical juxtaposition involves competing thermomechanicaldistortion between the sections 74/76. For instance, if a section isrelatively thin compared to an adjacent thicker section, there will beno thermomechanical juxtaposition because the thicker section willdominate and dictate the distortion. However, above a criticaldimension, the sections 74/76 cooperatively thermomechanically controlthe profile P. For example, the critical dimension is athrough-thickness, taken perpendicular to the axis L and a camber lineof the airfoil body 62, such that each of the sections 74/76 has athrough-thickness that is of approximately 20% or greater than thethrough-thickness of the airfoil body 62.

FIG. 5 shows a modified airfoil body 162. In this disclosure, likereference numerals designate like elements where appropriate andreference numerals with the addition of one-hundred or multiples thereofdesignate modified elements that are understood to incorporate the samefeatures and benefits of the corresponding elements. The second section176 of the airfoil body 162 tapers, as shown at 178, in a span-wisedirection along the longitudinal axis L. Alternatively, the secondsection 176 can terminate at a defined intermediate span of the airfoilbody 162, as shown at 180. For example, the defined intermediate span isthe middle third of the airfoil body 162.

FIG. 6 shows another modified example of an airfoil body 262. In thisexample, the first section 274 forms the first, pressure side surface 68of the airfoil body 262 and the second section 276 forms the second,suction side surface 70 of the airfoil body 262. There is a distinctboundary B between the sections 274/276 where the composition abruptlychanges between the sections 274/276.

In this example, if the second section 276 were to have a highercoefficient of thermal expansion than the first section 274, the profileP of the airfoil body 262 would have a tendency to curl or close withmore curvature from the illustrated contour upon an increase intemperature. Alternatively, if the second section 276 has a lowercoefficient of thermal expansion than the first section 274, the airfoilbody 262 would have the tendency to flatten or open with lessercurvature upon an increase in temperature. Thus, the sections 274/276cooperatively thermomechanically control the profile P responsive to thevarying thermal conditions.

FIG. 7 shows another modified airfoil body 362. In this example, theairfoil body 362 includes the first section 374, the second section 376,and a compositional gradient boundary section 382 between the firstsection 374 and the second section 376. In one example, thecompositional gradient boundary section 382 is a gradual change incomposition between the composition of the first section 374 and thecomposition of the second section 376. In another example, thecompositional gradient boundary section 382 is pre-selected mixture ofthe composition of the first section 374 and the composition of thesecond section 376, such as a 1:1 mixture.

FIG. 8 shows another modified example of an airfoil body 462. In thisexample, the second section 476 defines both the first side surface 68and the second side surface 70. In this example, the first section 474is a band that extends across the first side surface 68 and partiallycovers the first side surface 68. Alternatively, or in addition topartially covering the first side surface 68, the first section 474 canalso partially cover the second side surface 70. As can be appreciated,the geometry of the first section 474 can be tailored tothermomechanically control the profile P.

In FIG. 9, the first section 574 also partially covers the first sidesurface 68 of the second section 576 of the airfoil body 562 andincludes a cross-pattern. In FIG. 10, the first section 674 partiallycovers the second side surface 70 and has a wedge-like pattern thattapers along the span of the airfoil body 662.

A method of processing an airfoil having the features disclosed hereincan include an additive manufacturing process, although other techniquessuch as diffusion bonding, transient liquid-phase bonding or thermalspraying can alternatively or additionally be used. In additivemanufacturing, powdered metal suitable for aerospace airfoilapplications is fed to a machine, which may provide a vacuum, forexample. The machine deposits multiple layers of powdered metal onto oneanother. The layers are selectively joined to one another with referenceto Computer-Aided Design data to form solid structures that relate to aparticular cross-section of the airfoil. The composition of the powderedmetal can be varied for subsequent layers in order to provide thesections 74/76 and/or a compositional gradient, for example. In oneexample, the powdered metal is selectively melted using a lasersintering process or an electron-beam melting process. Other layers orportions of layers corresponding to negative features, such as cavitiesor openings, are not joined and thus remain as a powdered metal. Theunjoined powder metal may later be removed using blown air. With thelayers built upon one another and joined to one another cross-section bycross-section, an airfoil or portion thereof, such as for a repair, withany or all of the above-described geometries, may be produced. Theairfoil may be post-processed to provide desired structuralcharacteristics. For example, the airfoil may be heated to furtherconsolidate the joined layers.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this disclosure. The scope of legal protection given tothis disclosure can only be determined by studying the following claims.

What is claimed is:
 1. An airfoil comprising: an airfoil body includinga first section and a second section that differ in coefficient ofthermal expansion by at least 10% and that each have a through-thicknessthat is 20% or greater than a through-thickness of the airfoil body, thesecond section being arranged in thermomechanical juxtaposition with thefirst section such that the first section and the second sectioncooperatively thermomechanically control a profile of the airfoil bodyresponsive to varying thermal conditions.
 2. The airfoil as recited inclaim 1, wherein the first section and the second section are differentcomposition metallic materials.
 3. The airfoil as recited in claim 2,including a compositional gradient boundary between the first sectionand the second section.
 4. The airfoil as recited in claim 1, whereinthe first section and the second section are different compositionsselected from aluminum, aluminum alloys, titanium, titanium alloys,iron, iron alloys, nickel, nickel alloys, cobalt, cobalt alloys andcombinations thereof.
 5. The airfoil as recited in claim 1, including adistinct boundary between the first section and the second section. 6.The airfoil as recited in claim 1, wherein the first section is a coreand the second section is a shell circumscribing the core.
 7. Theairfoil as recited in claim 6, wherein the core terminates at anintermediate span between ends of the airfoil body.
 8. The airfoil asrecited in claim 7, wherein the first section and the second section aredifferent composition metallic materials.
 9. The airfoil as recited inclaim 8, including a compositional gradient boundary between the firstsection and the second section.
 10. The airfoil as recited in claim 7,wherein the core tapers along a span-wise direction of the airfoil body.11. The airfoil as recited in claim 1, wherein one of the first sectionand the second section has a suction side surface of the airfoil body,the other of the first section and the second section has a pressureside surface of the airfoil body, and the first section and the secondsection adjoin.
 12. The airfoil as recited in claim 1, wherein one ofthe first section and the second section has a pressure side surface andan opposed suction side surface, and the other of the first section andthe second section partially covers at least one of the pressure sidesurface and the suction side surface.
 13. A turbomachine comprising: anairfoil including an airfoil body having a first section and a secondsection that differ in coefficient of thermal expansion by at least 10%and that each have a through-thickness that is 20% or greater than athrough-thickness of the airfoil body, the second section being arrangedin thermomechanical juxtaposition with the first section such that thefirst section and the second section cooperatively thermomechanicallycontrol a profile of the airfoil body responsive to varying thermalconditions.
 14. The turbomachine as recited in claim 13, furtherincluding a turbine section that includes the airfoil.
 15. The airfoilas recited in claim 14, further including a compressor section and acombustor in fluid communication with the compressor section, theturbine section in fluid communication with the combustor.